introduction to db transparencies
TRANSCRIPT
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Chapter 1
Introduction to Databases
Transparencies
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Chapter 1 Objectives
u Some common uses of database systems.
u The characteristics of file-based systems.
u The problems with the file-based approach.
u The meaning of the term database.
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Chapter 1 Objectives
u The meaning of the term Database
Management System (DBMS).
u The typical functions of a DBMS.
u The major components of the DBMS
environment.
u The personnel involved in the DBMS
environment.
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Chapter 1 Objectives
u The history of the development of DBMSs.
u The advantages and disadvantages of DBMSs.
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File-based Systems
u A collection of application programs thatperform services for the end users (e.g.reports).
u Each program defines and manages itsown data.
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File-based Processing
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Limitations of File-based Approach
u Separation and isolation of data
Each program maintains its own set ofdata. Users of one program may be
unaware of potentially useful data held byother programs.
u
Duplication of data Same data is held by different programs.
Wasted space and potentially differentvalues and/or different formats for the
same item.
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Limitations of File-based Approach
u Data dependence
File structure is defined in the programcode.
u Incompatible file formats
Programs are written in different
languages, and so cannot easily accesseach others files.
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Limitations of File-based Approach
u Fixed Queries/Proliferation of applicationprograms
Programs are written to satisfy
particular functions. Any newrequirement needs a new program.
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Database Approach
u Arose because:
Definition of data was embedded inapplication programs, rather than being
stored separately and independently.
No control over access andmanipulation of data beyond that
imposed by application programs.
u Result - the database and DatabaseManagement System (DBMS).
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Database
u A shared collection of logically related data(and a description of this data), designed tomeet the information needs of an organization.
u System catalog (data dictionary or metadata)provides the description of the data to enableprogramdata independence.
u Logically related data comprises entities,attributes, and relationships of an
organization's information.
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Database Management System (DBMS)
u A software system that enables users todefine, create, and maintain the databaseand which provides controlled access to
this database.
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Database Management System (DBMS)
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Database Approach
u Data definition language (DDL).
Permits specification of data types,structures and any data constraints. All
specifications are stored in thedatabase.
u Data manipulation language (DML). General enquiry facility (query
language) of the data.
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Database Approach
u Controlled access to database mayinclude:
A security system.
An integrity system.
A concurrency control system.
A recovery control system.
A user-accessible catalog.
u A view mechanism.
Provides users with only the data theywant or need to use.
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Components of DBMS Environment
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Components of DBMS Environment
u Hardware
Can range from a PC to a network ofcomputers.
u Software
DBMS, operating system, network software(if necessary) and also the applicationprograms.
u Data
Used by the organization and adescription of this data called the
schema.
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Components of DBMS Environment
u Procedures
Instructions and rules that should beapplied to the design and use of the
database and DBMS.u People
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Roles in the Database Environment
u Data Administrator (DA)
u Database Administrator (DBA)
u Database Designers (Logical andPhysical)
u Application Programmers
u End Users (native and sophisticated)
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History of Database Systems
u First-generation
Hierarchical and Network
u Second generation
Relational
u Third generation
Extended Relational
Object-Oriented
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Advantages of DBMS
u Control of data redundancy.
u Data consistency
u More information from the same amountof data.
u Sharing of data.
u Improved data integrity.
u Improved security.
u Enforcement of standards.
u Economy of scale.
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Advantages of DBMS
u Balanced conflicting requirements
u Improved data accessibility andresponsiveness
u Increased productivity
u Improved maintenance through dataindependence
u Increased concurrencyu Improved backup and recovery services
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Disadvantages of DBMS
u Complexity
u Size
u Cost of DBMS
u Additional hardware costs
u Cost of conversion
u Performance
u Higher impact of a failure